This invention refers to a binary threshold comparator for use where the complement of the threshold number is available. A threshold comparator compares a first, varying, binary number with a second, threshold or reference, binary number and may be either of two types. A high threshold comparator indicates whether the first number (generally increasing) is greater than or equal to (greater/equal) the threshold or reference number. A low threshold comparator indicates whether the first number (generally decreasing) is less than or equal to (less/equal) the threshold or reference number. The two types are generally interchangeable in a circuit with some slight circuit modification and are thus considered equivalent.
The prior art in such comparators is shown in the circuit of FIG. 6. This circuit is for a single bit comparison and is seen to require 12 MOSFETs. An additional MOSFET would be required for the carry in terminal to establish the high/low threshold identity of the comparator, so that an eight bit version would require 8.times.12+1=97 MOSFETs.